1. Field of the Invention
The present invention relates to a new distinct Lactuca sativa romaine cultivar that exhibits resistance to lettuce drop (Sclerotinia minor) and tipburn.
2. Background of the Invention
Vegetables and especially lettuce have growing importance in the human diet. There are unique qualities to these foodstuffs that make them critically important to good health and longevity of life. Such vegetables are nearly exclusive eaten in their natural state as a fresh, raw product. As such the appearance of such vegetables is critical to their sale. Americans especially demand a perfect or near perfect appearance of their raw food products. Whereas, in some countries, foodstuffs can have blemishes and imperfections and be fit for the market, the US consumer demands a perfect near unblemished product.
Additionally, Americans are very demanding of the color of their food. Various is shades of color can determine whether a food product is successful at market. A deeper shade of green looks more appetizing than a pale shade of green or a green with a yellowish tint. A deep green in a ripe, healthy head of lettuce is especially desirable in a romaine lettuce and its varieties and has been found to be especially strong commercially.
It will be appreciated that all growers are faced with a limited amount of space in which to grow their vegetables and food products. It is more than desirable to maximize the yield of a particular parcel and especially so for the small to moderate sized grower. For example, if a grower can break even by selling about 500 cartons of lettuce per acre and he can switch to a different variety of the same lettuce and grow about 900 cartons of lettuce per acre, the product of the different variety would be much more valuable. This very well could be the difference between a grower able to survive bad economic conditions one year and continue his operation or going under and being forced to sell out or turn his land in residential property. Intense heat is considerably unfavorable for production of fresh market lettuce. Due to severe sun injuries, i.e. tipburn and scorching, no fresh lettuce is produced during the very hot early to late summer months in the San Joaquin Valley.
The export of vegetables across the international and state lines is vital to the grower. In 1998, lettuce was fifth among California""s top 20 crops with an estimated value of about $1.1 billion from 213,000 acres. In fact, California and Arizona grow about 90% of the total United States lettuce production and It is estimated that about 75% or more of all lettuce grown in California is so exported (Subbaroa 1998) for sale in states such as New York, Pennsylvania, Massachusetts and the like.
It is also traditional to export lettuce. Originally, lettuce was trucked from one location to another using ice to keep the lettuce fresh. This is how the name xe2x80x9cicebergxe2x80x9d lettuce came into being. Thus, not only is lettuce exported from the growing regions, but it has been so in the past and is likely to being for many future years as well.
For a further understanding of lettuce, its uses and history Waycott et al, U.S. Pat. No. 5,973,232 and Subbaroa 1998 is incorporated herein by references. There are six morphological types of lettuce: crisphead (iceberg), butterhead, Cos (romaine), leaf, stem and Latin. The crisphead is the most common in the United States, while butterhead and romaine types are popular in northern and southern Europe. Id.
Lettuce originated from the ancestral wild species L sativa. Today there are over one hundred cultivars, which are divided in commerce into four large groups based on gross morphological characteristics of the gross leaf morphology and leaf arrangement (Subbaroa 1998). These basic lettuce types frequently form the basis for grouping lettuces as is commonly seen in supermarkets, grocery and produce stores. Each of these basic groups is comprised of numerous cultivars; each characterized by its own particular morphology, disease resistance, and cultural adaptations.
Lettuce cultivars are susceptible to a number of diseases such as downy mildew (Bremia lactucae), lettuce drop (Scierotinia minor and S. scierotiorum), corky root (Rhizomonas suberifaciens), lettuce mosaic virus, big vein, and aster yellows, just to list a few. These diseases result in millions of dollars of lost lettuce crop through the world every year. In California alone, the average seasonal losses by lettuce drop, caused by Sclerotinia minor or Sclerotinia scierotiorum, is about 15% and may reach to about 60% or higher with heavy economic losses at higher lettuce prices. Lettuce drop effects all types of lettuce. There is no effective means of controlling lettuce drop and breeding host resistance cultivars remains the only logical option to manage the epidemiology of the disease.
The market quality of lettuce may also be influenced by abiotic factors. Tipburn disorder is one example. Tipburn incidence in lettuce is characterized by the presence of necrotic lesions at or near the margins of rapidly expanding inner enclosing mature leaves (Ryder 1998). Tipburn reaction is possibly related to a deficiency in plant calcium transport system along with reduced transpiration due to inner leaf enclosure. Inefficient concentration of calcium in the margins of rapidly expanding leaves may lead to cell wall breakdown and the occurrence of large to small lesion formation (Collier and Tibbitts 1982, Barta and Tibbitts 2000). Depending on the severity of tipburn at market stage, the grower may be entitled to lower market price or loss of the entire crop. Development of tipburn injury symptoms may occur when the daytime temperature ranges from 32 to 40 C (Ryder 1998). Plants may exhibit considerable tipburn injury at or near the market stage especially when the inner mature leaves have completely enclosed or cupped in. Lettuce cultivars with resistance to tipburn are highly desired by the growers.
In order for lettuce to be fit to travel to other states, each head of lettuce must pass a vigorous inspection. A part of the inspection calls for the lettuce plants to be free of rot, decay or tipburn. Even a small amount of rot or tipburn can open the door to an infection for the entire shipment. Thus, not just the infected plant or plant(s) are banned from travel across state lines, but the entire lot of lettuce will be prohibited should evidence of such lettuce drop or tipburn be found.
In order to be commercially viable, a grower must then be able to produce a sufficient quantity of plants that are healthy and fit for travel. The yield of the grower""s acreage will determine the grower""s financial success and whether he can continue his operation in the face of rising competition and market driven demands.
What is therefore needed is a lettuce plant variety that allows the grower to maximize his yield and provide plants that are desirable to the consuming public. It is also desirable to provide the lettuce grower with a lettuce plant that not only maximizes his yield and extends the growing season into the hot summer months, but also yields a plant, which is fit for travel across interstate lines. And, it is desirable to provide the lettuce grower with a lettuce plant which generates strong consumer sales by having the sought after color and appearance.
It is a general object of this invention to provide a new distinct romaine Lactuca sativa cultivar, which increases yield to growers.
It is another object of this invention to provide a new distinct romaine Lactuca sativa cultivar, which not only increases yield but also provides a pleasing and commercially desirable dark green color.
It is another object of this invention to provide a new distinct romaine Lactuca sativa cultivar, which not only increases yield but also with superior resistance to tipburn.
It is another object of this invention to provide a new distinct romaine Lactuca sativa cultivar, which not only increases yield but also with superior resistance to lettuce drop caused by fungal agent Sclerotinia minor. 
It is yet another object of this invention to provide a new distinct romaine Lactuca sativa cultivar, which not only increases yield but also has a wide core diameter with a smaller core length.
The present invention comprises a new distinct romaine Lactuca sativa cultivar herein xe2x80x98Thermo Cosxe2x80x99. Thermo Cos exhibits increased resistance to lettuce drop and tipburn. In addition, xe2x80x98Thermo Cosxe2x80x99 has a leaf color of Value 4 Chroma 4 Hue 7.5GY according to the Munsell Color Chart for Plant Tissues. In average, mature market stage heads of xe2x80x98Thermo Cosxe2x80x99 weigh about 730 grams compared to 752 grams for the closest comparable variety, King Henry, Plant Variety Protection Pending Number: 9600323 which is commercially available from Progeny Advanced Genetics, Inc. Salinas, Calif., 93907. Seeds of xe2x80x98Thermo Cosxe2x80x99 have been deposited with a public depository agency the American Type Culture Collection (ATCC), 10801 University Boulevard, Manassas, Va. 20110-2209 under the Budapest treaty on Mar. 20, 2000 and have assigned Accession number PTA-2252.
The present invention relates to a Lactuca sativa plant produced by growing the seed of xe2x80x98Thermo Cosxe2x80x99 that has ATCC Accession No. PTA-2252. The present invention also relates to a Lactuca sativa plant that has all the physiological and morphological characteristics of a Lactuca sativa plant grown from seed from ATCC Accession No. PTA-2252.
Finally, the present invention relates to a hybrid Lactuca sativa plant having xe2x80x98Thermo Cosxe2x80x99 as a parent.